In the current automobile engines, oxidation catalysts, three-way catalysts, NOx storage reduction catalysts, diesel particulate filters (DPF's), and the like are used in order to clean the exhaust gas.
It has been known that those post-cleaning devices for the exhaust gas are adversely affected by a metal component, a phosphorous component, and a sulfur component in the engine oil, so it goes without saying that those components are preferably reduced as much as possible.
Further, reduction of the metal component, the phosphorous component, and the sulfur component in the engine oil is preferred with a view to controlling catalyst degradation.
As the anti-wear agent in the engine oil, zinc dialkyl dithiophosphate has been used for a long time and is considered to be an essential additive at present too.
The zinc dialkyl dithiophosphate contains a metal component, a phosphorous component, and a sulfur component. Therefore, the decomposed substances of the zinc dialkyl dithiophosphate become sulfuric acid and phosphorous acid, and lead to consumption of the basic compound in the engine oil, with the result that oil change intervals become extremely short. In view of the forgoing, an alternative anti-wear agent is demanded.
The same is also true of other lubricating oils except for the engine oil.
Examples of applying heterocyclic compounds to lubricating oils are described in the patent documents below.
In Patent Document 1, benzotriazole is used as a corrosion inhibitor.
Patent Document 2 describes the application of a triazole derivative to a refrigerator oil composition and insists on the effect of wear resistance.
In Patent Document 3, an imidazole fluorine derivative is used as a surface-treatment agent.
Patent Document 4 describes that polybenzoimidazole is used as a polymer including an internal lubricant.
In Patent Document 5, there is a description relating to a fluid composition for an active suspension that contains thiadiazole and benzotriazole and is excellent in wear resistance.
Patent Document 6 describes that a triazine derivative is used as a dispersant for a lubricant and a fuel.
Patent Document 7 describes an indazole thione additive used for a lubricant.
Patent Document 8 describes a fluid having low traction property and having a triazine structure.
Further, Patent Document 9 describes a wear resistant lubricant composition containing a triazine derivative.
In Patent Document 10, a substituted thiophene is used as an anti-wear agent used in a freon compressor.
Patent Document 11 describes a substituted pyridine derivative and a substituted diazine derivative as heterocyclic compounds.
However, the described compounds do not achieve a demanded wear resistance level and have problems for practical use.    Patent Document 1: JP 64-29497 A    Patent Document 2: JP 06-100881 A    Patent Document 3: JP 06-157471 A    Patent Document 4: JP 07-506860 A    Patent Document 5: JP 08-165483 A    Patent Document 6: JP 2002-534436 A    Patent Document 7: JP 2003-505577 A    Patent Document 8: JP 2004-315703 A    Patent Document 9: JP 2004-331950 A    Patent Document 10: JP 58-103594 A    Patent Document 11: JP 62-243692 A